Cleanable tube within a tube heat exchanger and method of forming modular headers therefor

ABSTRACT

Inner and outer headers at both ends of a tube within a tube heat exchanger are formed of a plurality of axially stacked and brazed drawn metal tubular shell segments. Segments for all headers are identical and carry axially aligned large diameter and small diameter holes on opposite sides thereof for facilitating reception of the inner tube coupling the outer headers and the outer tube coupling the inner headers as well as bushings receiving removable plugs to facilitate cleaning of the interior of the inner tubes of the heat exchanger tube assemblies.

United States Patent Schwarz [451 Dec. 12,1972

[54] CLEANABLE TUBE WITHIN A TUBE HEAT EXCHANGER AND METHOD OF FORMINGMODULAR HEADERS THEREFOR [72] Inventor: Leonard H. Schwarz, WestHartford,Conn,

[73] Assignee: Dunham-Bush, Inc., West Hartford,

Conn.

[22] Filed: July 7, 1970 21 Appl. No.: 52,902

[52] US. Cl; ..165/143 [51] Int. Cl.L.. ..F28d 7/10 [58] Field ofSearch. ..165/l43, 151

[56] References Cited UNITED STATES PATENTS 2,658,358 11/1953 Bolling..165/l43 X 10/1934 Feldmeier ..l65/l43 X 3/1967 LaPorte et al...l65/l5l X Primary Examiner-Frederick L. Matteson AssistantExaminer-Theophil W. Streule Attorney-Sughrue, Rothwell, Mion, Zinn &Macpeak [5 7 ABSTRACT Inner and outer headers at both ends of a tubewithin a tube heat exchanger are formed of a plurality of axiallystacked and brazed drawn metal tubular shell segments. Segments for allheaders are identical and carry axially aligned large diameter and smalldiameter holes on opposite sides thereof for facilitating reception ofthe inner tube coupling the outer headers and the outer tube couplingthe inner headers as well as bushings receiving removable plugs tofacilitate cleaning of the interior of the inner tubes of the heatexchanger tube assemblies.

5 Claims, 5 Drawing Figures PAIENTED DEC 12 m2 SHEET 1 BF 2 FIG. 3

FIG. I PRIOR ART FIG. 5

INVENTOR LEONARD H. SCHWARZ ,M/hg a y W ATTORNEYS PATENTEDUEC 12 I972SHEU 2 (IF 2 DESCRIPTION OF THE PRIOR ART In the past, multi-pass heatexchangers such as condensers have been manufactured by employingprincipally, three U-shaped interfitting brass members formed of thinplate stock to define an integral header assembly, that is, an outerheader carrying the coolant and an inner head carrying refrigerant for amulti-pass refrigeration condenser or the like with header assemblies ateach end of the heat exchanger. Respective headers are'fluid coupled bymeans of the concentric tube within a tube assemblies extending betweenthe same with the large diameter outer tube coupled to the inner wall ofthe inner headers and the small diameter internal tube extending axiallybeyond the ends of the large diameter tube and coupled to the outerheader by extending through a small diameter hole formed within theintermediate wall separating the two headers.

Reference to FIG. 1 discloses a typical multi-pass condenser headerassembly for a condenser of the tube within a tube type construction. Assuch, the prior art header assembly is formed principally of three U-shaped brass members stamped from thin metal flat stock and consistingof a large outside U-shaped member 12, an intermediate U-shaped member14 and an inner U-shaped member 16, members 12 and 14 being nested andfacing in the same direction while member 16 is nested within member 14,but facing in the opposite direction. Brazed rings 19 defining largediameter openings 18 within end wall 20 of member 12 are then brazed tothe ends of the large diameter tubes (not shown), and further smallrings 23 defining smaller diameter holes 22 within the end wall 24 arebrazed to the small diameter tubes (not shown). Similar diameter holes26 within end wall 28 of the reversely oriented U-shaped member 16,carry the internally threaded fittings 30 which receive removable endplugs (not shown). This allows the passage of cleaning elements withinthe threaded bore 32 of the same for entry into the small diameter tubesof the tube assemblies (not shown) connecting headers at respective endsof the heat exchanger. In addition, in such an assembly it is necessaryto provide baffle plates 34 at various positions within both the outerheader created by plates 16 and 14 and the inner header created byplates 12 and 14 to cause the fluid within the same to move alongdesired flow paths from a header at one end of the heat exchanger to theheader at the opposite end and thence return to the same header butwithin another area separated by the baffle plates 34. In the case ofFIG. 1, the return fluid would exit from the chambers on the upper sideof plates 34, pass to the other end of the heat exchanger and return toenter the chambers defined by the lower side of the same baffle plates34.

In the manufacture of such heat exchangers, it is necessary to build upthe header by brazing the three primary plates together, that is, l2, l4and 16, and braze rings 19 and 23 thereto to define openings 18 and 22,and further braze the baffle plates 34 in proper position to define thenumber of passes for the heat exchanger. Since the joints existingbetween all of these components must be sealed to create sealedcompartments, it is very difficult to complete a sealed brazed assemblyexcept by a series of subassembly, brazing and leak testing steps and,perhaps more importantly, upon completion of the heat exchanger,including the brazing ofthe inner and outer tubes to respective openings18 and 22, it is impossible to repair any internal leaks between rise orheader chambers or in the vicinity of the baffle plates 34, nor in factis it possible to determine just where the leaks have occurred, since agreat number of the joints are hidden, in this type of construction.

SUMMARY OF THE INVENTION The present invention is directed to theproduction of a readily cleanable, tube within a tube heat exchanger inwhich all brazed joints are exposed to the outside and in which thecompletion of the brazed assembly may be achieved by only a few separatebrazing steps and with greatly increased reliability. The inventionallows ready use of identical components to form a modular heatexchanger of variable height and in which identically formed assembliesmay be stacked back to back, and fluid coupled to effect a compact,large capacity heat exchanger.

The present invention resides primarily in the creation of fouridentically configured headers, each comprising a plurality of axiallystacked and brazed drawn metal, tubular shell segments with each segmentconstituting a-tubular body having open ends and diametrically opposedlarge diameter and small diameter holes defined by integral rims. Innerand outer headers are formed at each end of the heat exchanger byplacing the stacked shell segments with their small diameter holesfacing each other. Concentric tube assemblies with the inner tubeextending beyond the end of the outer tubes, are inserted therein, suchthat the ends of the large diameter tube are brazed. to the shellsegment where the large diameter hole of the inner header faces the sameand wherein the small diameter inner tubes of each tube assembly extendthrough both small diameter holes of the inner and outer header and arebrazed to the integral rims defining the same. The large diameter holesof the outer header segments at each end of the assembly carry brazedthereto a threaded bushing receiving a threaded removable end plugallowing access of cleaning equipment to the inner tube of the tubeassembly to facilitate cleaning of the same.

Domed end caps are readily brazed to the upper and lower ends of each ofthe headers to complete the same with some of the caps being providedwith conventional fluid coupling fittings allowing delivery and removalof the heat exchange fluids to respective headers. Disc shaped baffleplates are brazed between selected tubular shell segments to define thepasses for the fluids passing through the concentric tube assembliescoupling headers at the opposite ends of the heat exchanger. Preferably,the cup-shaped drawn metal shell segments have enlarged diameter lips atone end to both receive the opposite end of the adjacent segment andalso to facilitate the holding of the discshaped baffle plates which areslightly larger in diameter than the major portion of the shell segmentsto facilitate placement and brazing of the same. Since all joints areexposed to view, any seal failures are readily ascertainable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view,partially in section, of a prior art header assembly for use in forminga tube within a tube heat exchanger.

FIG. 2 is a side elevational view, partially in section, of the improvedtube within a tube heat exchanger of the present invention employingstacked drawn metal tubular shell segments to define inner and outerheaders at both ends of the heat exchanger.

FIG. 3 is an end view, partially in section, of the heat exchanger shownin FIG. 2.

FIG. 4 is an exploded, perspective view of a portion of one header ofthe heat exchanger of FIG. 2, illustrating the use of the drawn metalshell segments of the present invention.

FIG. 5 is a sectional view of a tube within a tube" heat exchanger tubeassembly coupling the headers at respective ends of the heat exchanger.

DESCRIPTION OF THE PREFERRED EMBODIMENT In contrast to the heat exchangeheader assembly of the prior art illustrated in FIG. 1, the presentinvention makes use of a plurality of stacked, drawn metal tubular shellsegments 40 as seen in FIG. 4, which are formed from fiat metal stockand drawn by conventional methods.

In FIG. 2, for each segment 40, an open top 42 and an open bottom 44 isshown. It is noted that the open top 42 is defined by an enlargeddiameter lip 46 which allows the seating of the bottom edge of theadjacent cup within the same so as to define a stacked array for theindividual headers identified at A, B, C, and D, headers A and D beingthe outer headers while headers B and C are the inner headers of theheat exchanger. The open bottom, cup-shaped segments 40 for all headersA, B, C, and D, are identical in size and configuration and are alsoidentically formed with a large diameter hole 48, FIG. 2, punched intothe side thereof with some of the material defining an integral internalrim 50, while in similar fashion, small diameter holes 52 are formed bypunching the side wall inwardly and forming a small diameter rim 54.The'large diameter holes 48 receive cylindrical bushings 56 which arebrazed thereto and carry, in turn, removable threaded plugs 58 andwashers 60 so as to effect a ready seal of the end plugs 58 when seatedwithin the threaded busing 56.

The bushing and plugs are carried in all of the large diameter holes ofthe segments of the exterior headers, since removal of the plugs allowsready access to the interior of the outer header A and D and insertionof a cleaning tool (not shown) within the same. Inner headers B and Care oppositely oriented to outer headers A and D, that is, the smallerdiameter holes 52 for these headers lie side by side and in axialalignment. It is by this arrangement, that each small diameter hole 52receives the axially extending end 62 of the small diameter tube 64,forming a portion of a tube within a tube heat exchanger tube assembly66. The outer tube 68 is formed of suitable metal, and the refrigerantis carried by the outer passage defined by the large diameter tube 68and the small diameter tube 64. A corrugated metal fin 70 is wrapped inspiral fashion about the small diameter inner tube 64, and facilitatesheat exchange between the fluid flowing through small diameter tube 64and the counterflow fluid between this tube and the large diameter tube68. The protruding ends 62 of the small diameter tube are brazed to theannular rims 52. The length of the large diameter tube 68 is such thatit extends within headers B and C and is brazed to the periphery of rim50 defining opening 48 of the inner headers B and C.

It is, therefore, apparent that if incomplete brazing occurs at thejoints between the large diameter tube 68 and rim 50 receiving the same,or the small diameter tubes and rims 52 for all four headers, or ifthere is incomplete brazing and a lack of seal between bushing 56 andrim 50 of the outer headers A and D, the exact spot where leakageoccurs, being exposed, may be ascertained for prompt repair of the heatexchanger at the specific area requiring the same.

Of course, the heat exchanger has the further advantages, since itemploys thin metal baffle discs or plates 72 which define the number andextent of passes of both coolant and refrigerant within respective tubes64 and 68, of each tube assembly 66. Since the diameter of the baffledisc 72 is larger than the internal diameter of the major portion of theshell segment, but is slightly less than the diameter of the enlargedrim portion 46 of the segments, they may be merely dropped in placealong with suitable brazing material at the proper position in thevertical stack. When brazed, they effect a sealed joint while at thesame time adjacent segments are sealingly coupled to facilitate bothease in assembly and time required to effect brazing of the componentsinto multi-pass modular headers. During manufacture, the complete headerassembly may be formed by properly stacking shell segments upon eachother with spacers or baffles 72 at predetermined locations. Afterbrazing the four headers A, B, C, and D, a vertical assembly may beformed much in the manner of that of the completed unit shown in FIG. 2.Domeshaped end caps 74 or perforated end caps 76 which carry elbowfitting 78 and allowing fluid connection to the supply of coolant andrefrigerant for a condenser use, and discharge of the same at theopposite ends of respective headers, are brazed to the ends of eachheader to achieve, respectively, a sealed connection and a completelysealed assembly. The heat exchanger of FIG. 2 is shown with an enlargedfitting adapter and an enlarged pipe plug 83 carried by the same,providing an enlarged diameter opening for coupling to an additionalcoolant supply from a water tower.

It is important to note that when metal drawing the cup-shaped elementstherefrom to define segments which are open both at the top and thebottom, the holes through the cylindrical wall as at 48 and 52 and therims 50 and 54 defining the same may be readily formed since the end ofthe short tubular segment allows insertion of a forming tool internallyof the same, while the other open end allows the waste material to bedischarged therefrom during forming of the punched holes 48' and 52.With the shell segments being drawn from sheet metal stock, allconnections to fittings and the tubes of the heat exchanger assembly 66may be readily brazed by a conventional fluxed or fluxless brazing alloywhich is compatible both to the water forming the coolant and aconventional refrigerant carried by the large diameter outer tube 68 andinner headers B and C, respectively. The heat exchanger is formed of asingle or multiple layers of vertically stacked arrays of tubeassemblies 66 fluid coupled to inner and outer headers A, D, and B, C.It may be readily supported by L-shaped heat exchangers supports 80having a common base 82 and a pair of side walls 84 coupled together byscrews 86 which pass between adjacent tube assemblies 66. In a samplearrangement, FIG. 3, more than one vertical stack of tube assemblies 66and headers are provided. Thus,in-addition to the tube assemblies 66making up the first row of the heat exchanger, one or more additionalrows of tube assemblies 66, constitutes a multiple series of heatexchange passages defined by inner tubes 64 and outer tubes 68.

The v present invention contemplates unique mechanical connection meansfor supporting additional vertical stacked arrays of tubes just to therear of the first stack. The mechanical means consists of a series'ofthreaded bolts 90 which carry modified spacer discs 92 having curvedrecessed inner surface portions 94 which abut the outside surfaces ofthe outer tube 66 with a modified disc 92' captured between the tubeassemblies 66 for each vertical stack and having two cylindricalrecesses within each end face abutting respective tubes of the adjacentrows. As seen in FIG. 2, on the opposite side of the heat exchanger,similar discs 92 are provided, and a threaded nut 96 completes themechanical connection. Thus, with four such bolts and a series of spacerdiscs, at respective corners of the heat exchanger, multiple verticalarrays of heat exchange tube assemblies, may be mechanically coupledtogether for fluid connection by various connecting means (not shown) sothat fluid may flow either in series through these tubes, or inparallel, as desired.

In operation, refrigerant gas passes through fitting 78 identified at F,FIG. 2, and enters header B where, due to the presence of the firstbaffle disc 72, the refrigerant passes through the upper two, largediameter tubes 68, where it enters the larger volume chamber withininner header C, as defined by uppermost baffie disc 72 carried thereby.The refrigerant continues to pass in a reverse direction through thenext two tubes assemblies 66 and re-enters a chamber defined by the twoupper discs 72, in header B. At this point, the gas returns to the rightside of the assembly, that is, the inner header C through a single tubeonly, and flow continues in this manner until the condensed refrigerantis discharged through fitting H at the lower left hand side of header B.The coolant, employed to achieve condensation of the refrigerant,preferably enters fitting G at the bottom end of header A and passeswithin small diameter tube 64 of the lowermost tube assembly 66 andenters the right hand header D, where it reverses direction along a passdefined by the lowermost baffie discs 72 carried by header D. Flowcontinues as determined by baffle discs 72. The heated coolant liquid,such as water, is discharged from the heat exchanger through elbowfitting E at the upper end of header A. Of course, for the next array ofheat exchanger tubes to the rear of the illustrated array, FIG. 2, fluidmay be passing in parallel or in series as desired.

Further, while the heat exchanger is advantageously manufactured by theuse of the drawn, modified cuplike shell segments 40, which areidentically formed but oppositely oriented insofar as the inner andouter headers are concerned, it is envisioned that long metal tubesdefining each header may be severed at various locations to facilitateplacement of the baffie 72 into position, and then brazed, and likewisemay have a series of large diameter and small diameter holes drilled orotherwise formed therein before or after severing, but the arrangementof the same allows unimpeded inspection of all brazed joints between thebaffle plates and the header tubes, and the tube assemblies of the heatexchanger coupling the headers at opposite ends of the same.

What is claimed is:

1. In a tube within a tube heat exchanger including inner and outerfluid headers sealingly coupled, respectively, to opposite ends of innerand outer tubes defining a heat exchange tube assembly, the improvementwherein:

each header comprises a plurality of open ended,

identical, axially stacked, tubular segments in module form, eachsegment including opposed small and large diameter holes within its sidewall, respective headers at each end of said tube assembly beingoriented with their small diameter holes facing each other, each smalldiameter tube extending beyondthe ends of said large diameter tube foreach tube assembly and passing through both small diameter holes foreach header, and sealed thereto, each large diameter tube being sealedwithin a largediameter hole of said inner header and removable end plugssealingly carried by said large diameter holes within said outer headerto facilitate cleaning of said small diameter tubes while allowing easylocation of any loss of seal between the sealed components of said heatexchanger.

2. The tube within a tube heat exchanger, as defined in claim 1, whereineach tubular segment comprises a cylindrical drawn metal body having anenlarged rim on one end to facilitate stacking and an imperforate baffiedisc within saidenlarged annular lip of selected segments as well as theend of the adjacent shell segment to facilitate seal coupling of theseelements while forming the flow paths of said heat exchange fluidsthrough said heat exchanger.

3. The tube within a tube heat exchanger, as claimed in claim 1, whereinsaid tubular segments are drawn from thin metal material, and said smalland large diameter holes are formed by punching in portions of saidtubular segment side wall to define an annular rim coaxial with eachhole.

4. The tube within a tube heat exchanger, as claimed in claim 3, whereinthe axial ends of said headers are closed off by domed-shaped end capssealed thereto.

5. A multiple row, readily cleanable, tube within a tube heat exchangerassembly characterized by completely exposed brazed joints throughoutthe assembly, comprising: pairs of inner and outer substantially tubularfluid headers brazed to opposite ends of inner and outer tubes definingheat exchange tube assemblies for each vertical array, each of saidheaders constituting a plurality of identical open ended, cupshaped,axially stacked drawn shell segments, each segment including opposedsmall and large diameter holes within its sidewall, respective headersat each end of said tube assemblies being oriented with their smalldiameter holes facing each other to commonly receive an end of saidsmall diameter tube extending beyond said large diameter tube and beingbrazed thereto, the large diameter tubes extending within the largediameter hole within said inner headers and brazed thereto, said largediameter holes within said outer header carrying removable threaded endplugs for facilitating cleaning of the inner tubes of said heatexchanger, and a plurality of mechanical coupling means for coupling atleast two vertical stacked arrays, said coupling members comprising athreaded bolt extending between adjacent large tubes of the heatexchanger tube assemblies for all vertical stacked arrays the width ofsaid heat exchanger assembly, and a plurality of spacer discs carried onsaid threaded bolt with at least one spacer disc between each verticalstacked array and having arcuate grooves corresponding to the peripheryof the outer tube of said tube assembly and being of a thickness tospace said vertical stacked array of tube assemblies from each other anda nut for mechanically locking said spacers to said tube assemblies.

' a: wr

1. In a ''''tube within a tube'''' heat exchanger including inner and outer fluid headers sealingly coupled, respectively, to opposite ends of inner and outer tubes defining a heat exchange tube assembly, the improvement wherein: each header comprises a plurality of open ended, identical, axially stacked, tubular segments in module form, each segment including opposed small and large diameter holes within its side wall, respective headers at each end of said tube assembly being oriented with their small diameter holes facing each other, each small diameter tube extending beyond the ends of said large diameter tube for each tube assembly and passing through both small diameter holes for each header, and sealed thereto, each large diameter tube being sealed within a large diameter hole of said inner header and removable end plugs sealingly carried by said large diameter holes within said outer header to facilitate cleaning of said small diameter tubes while allowing easy location of any loss of seal between the sealed components of said heat exchanger.
 2. The ''''tube within a tube'''' heat exchanger, as defined in claim 1, wherein each tubular segment comprises a cylindrical drawn metal body having an enlarged rim on one end to facilitate stacking and an imperforate baffle disc within said enlarged annular lip of selected segments as well as the end of the adjacent shell segment to facilitate seal coupling of these elements while forming the flow paths of said heat exchange fluids through said heat exchanger.
 3. The ''''tube within a tube'''' heat exchanger, as claimed in claim 1, wherein said tubular segments are drawn from thin metal material, and said small and large diameter holes are formed by punching in portions of said tubular segment side wall to define an annular rim coaxial with each hole.
 4. The ''''tube within a tube'''' heat exchanger, as claimed in claim 3, wherein the axial ends of said headers are closed off by domed-shaped end caps sealed thereto.
 5. A multiple row, readily cleanable, tube within a tube heat exchanger assembly characterized by completely exposed brazed joints throughout the assembly, comprising: pairs of inner and outer substantially tubular fluid headers brazed to opposite ends of inner and outer tubes defining heat exchange tube assemblies for each vertical array, each of said headers constituting a plurality of identical open ended, cup-shaped, axially stacked drawn shell segments, each segment including opposed small and large diameter holes within its sidewall, respective headers at each end of said tube assemblies being oriented with their small diameter holes facing each other to commonly receive an end of said small diameter tube extending beyond said large diameter tube and being brazed thereto, the large diameter tubes extending within the large diameter hole within said inner headers and brazed thereto, said large diameter holes within said outer header carrying removable threaded end plugs for facilitating cleaning of the inner tubes of said heat exchanger, and a plurality of mechanical coupling means for coupling at least two vertical stacked arrays, said coupling members comprising a threaded bolt extending between adjacent large tubes of the heat exchanger tube assemblies for all vertical stacked arrays the width of said heat exchanger assembly, and a plurality of spacer discs carried on said threaded bolt with at least one spacer disc between each vertical stacked array and having arcuate grooves corresponding to the periphery of the outer tube of said tube assembly and being of a thickness to space said vertical stacked array of tube assemblies from each other and a nut for mechanically locking said spacers to said tube assemblies. 